Lessons in "Outdoor Wood"

Pressure-treated wood is truly a "wood for all seasons"... a rugged exterior building product
that's rot and insect resistant. If Noah's ark was made from this stuff, it would still be cruising the Mediterranean!

Treated wood is used for
decks, mailbox and light posts, swing sets and playscapes, picnic tables,
landscape ties, underwater dock pilings, oceanside boardwalks, telephone utility
poles and, believe it or not, residential building foundations in some parts of
the country!

You can purchase pressure-treated (PT) wood as lumber, boards, posts, and
even plywood! Its unique ability to fend off decay makes it ideal in any high
moisture and/or ground contact installations.

Yet, there is much misinformation, and, in some cases, disinformation
concerning pressure-treated wood, its maintenance requirements, and its safety
in common use. Let's explore the story of pressure-treated wood, and together
seek out the truth.

If you wonder whether you should use PT wood for a raised garden frame, click
HERE.

What is pressure-treated wood?

Over 70 years ago, Dr. Karl Wolman invented the process of infusing
preservative deeply into wood products. Today, a giant industry has grown up
around his quest to invent a wood that can last forever.

Pressure treating is a process that forces a chemical preservative deep into
the wood. The wood product is placed into a humongous cylindrical holding tank,
and the tank is depressurized to remove all air. The tank is then filled with
the preservative under high pressure, forcing it deeply into the wood. The tank
is then drained and the remaining preservative reused. The wood is removed from
the tank and prepared for shipment to your local lumberyard.

Needless to say, this process makes the wood quite unappetizing to all
vermin, insects, and fungus, which accounts for its 20 year plus lifespan under
the harshest conditions!

This information is required to be posted on each board and is either
marked with ink on the board or on a plastic tag that is stapled onto the end of
each treated board. Generally speaking,
this is not something for you to be concerned with, since your local lumberyards
will only carry the types suitable to your climate. Always let the
salesman know the eventual location of the PT lumber... above, on or below
grade... so that you can make the best purchase!

What is the chemical preservative used, and is it dangerous?

Until 2003, the preservative most commonly used in residential
pressure-treated lumber
was chromated copper arsenate (CCA), an extremely toxic chemical. Remember
"Arsenic and Old Lace"? How about that old box of rat poison you have
lurking in the garage? CCA is so toxic that the Environmental Protection Agency,
over 20 years ago, imposed strict guidelines regarding the manufacturing
practices of companies using CCA.

However, one must distinguish between the toxicity of the chemical and the
toxicity of the wood product in everyday use. Extensive studies were done
since the mid 1980's concerning the potential dangers of pressure-treated wood,
and rightfully so! Large volumes of CCA were being used, and the treated wood
products were beginning to be widely distributed, justifying the need for some
hard research.

The research was mixed, but the typical hysteria ensued as attorneys and
plaintiffs lined up to claim damages from exposure to CCA. In the end, the
industry agreed to voluntarily eliminate use of CCA for residential use.
CCA is still being used in certain marine and industrial applications since it
is still the best preservative available at the present time.

The new alternatives to arsenic-based preservatives.

Your local home store or lumberyard is now selling lumber treated with less
toxic alternatives... amine copper quat (ACQ) and copper azole
(CA)... though you may find other chemical combinations in specific areas.
The reason these new copper-based alternatives are considered safer than
arsenic-based preservatives is based on the human body's inability to absorb these
poisons. Inorganic arsenic is readily absorbable by the body.

Whether these new chemicals will turn out to be less hazardous in the long
term is anyone's guess, but all indications are that they will be. Fingers
crossed!

Is the copper-based preservative as good as the
arsenic-based preservative?

Yes, from what I've read overall the replacements are equivalent, but
copper-based preservatives are mucho more expensive. To keep PT wood
affordable,
manufacturers are lowering the amount of preservative for boards used in less
demanding applications. For example, 5/4" boards typically used for
decking will receive less preservative than 2x boards which will be rated for
above ground use. 4x4 and 6x6 and larger beams and posts will receive a
ground contact rating.

What that means is if your lumberyard does not carry 2x lumber with the
proper amount of preservative (for ground contact) and you use it for a raised
garden or bury it, you might find the material rotting in short order.
Albeit not as quickly as untreated lumber, but far from the decade plus that the
older PT wood could last.

Are there any special considerations when using wood
with a copper-based preservative?

Following the safety rules (below) regarding cleanup should be sufficient.
However, these newer products are extremely corrosive to steel and aluminum.
Fasteners and construction hangers/ties should be rated for use with the new
wood. Any aluminum flashing should be covered with an impervious layer of
a non-corrosive material such as tar paper or non-permeable plastic sheets to
prevent contact with the wood.

If CCA is potentially dangerous, should I tear out my
old deck? It's otherwise in great shape.

Absolutely not. Existing decks pose no danger and, in fact, tearing
them out may release more chemical than leaving them in place! (See the
safety precautions below.)

The EPA has stated that applying a penetrating oil finish as
needed to pressure-treated wood surfaces (that have human contact) can lessen or
eliminate human and animal exposure to CCA in existing decks. Studies done
to date show a dramatic decrease in the amount of arsenic at the surface of the
wood for periods up to two years when compared with unsealed wood.

What are the safety precautions regarding use of pressure-treated wood?

The sawdust from pressure-treated wood can be an irritant to the nose,
eyes, and skin.
Use of a dust mask and eye protection is highly
recommended. Prevent contact with the skin as much as possible.

Try to collect as much of the sawdust as possible for disposal.If possible, do most of your cutting in a specified location, and lay a
heavy disposable plastic tarp under your saws or sawhorses. Use of a tarp is
especially valuable if you must cut in an area that you cannot easily sweep,
such as a lawn. Actually, this is a cleanup timesaver you can use even when
cutting ordinary boards, especially if you generate large amounts of dust,
as in making rip cuts!

Pressure-treated wood should
not be burned except by professionals.
Other products that are on the
do-not-burn list are plywood, particleboard, chipboard and painted or
finished wood. To be fair, there was one government study that did not find
any more toxicity in the smoke from pressure-treated wood than from regular
wood. The ash, though, was definitely more toxic, because the arsenic does
not burn off. So you wouldn't want to add this ash to soil or your compost
heap. All of us who have heated their homes with wood know how the ash is
everywhere and on everything!

Do not use pressure-treated wood for making cutting boards, or for any
food preparation surface.
Picnic tables made of pressure-treated wood
have
become common, and are fine to use for the purpose they were intended... to serve
food on (or play cards on), not to prepare food on! They should
be coated as needed with an oil-based wood preservative (not paint or opaque
stain) to seal in the
chemical preservative.

Pressure-treated wood is intended for outdoor use only!
There
are a few exceptions to this rule, though you should check with your local
building inspector to be sure. First is the use of pressure-treated wood in place of
Douglas fir for sill plates in new construction. Sill plates are the
lowest framing boards in a wood home. They are bolted to the top of the
foundation (so the next windstorm doesn't hurl your house to Oz!), and the
house is erected onto them. Dampness in the poured concrete foundation can be
absorbed by the sill plate, making it attractive to carpenter ants and
termites. pressure-treated wood is resistant to termites and unappetizing to
ants, so its use can help convince the little critters to go next door for
dinner.

The second is for so-called permanent wood foundations, and the
third is to replace the bottom plate on wall framing in basements or other
below grade applications, especially when the bottom plate is resting directly
on a concrete foundation subject to dampness. In both these cases, PT
wood is essential to prevent rot and lengthen the life of the job.

Why does pressure-treated wood need to be
coated with a preservative? If it's so dang tough, why bother?

Though the infused preservative prevents rot, it does not inhibit weathering...
The effects
of the elements on pressure-treated wood are no different than with ordinary
wood. So a preservative is a must, and should be applied as soon as possible
after your project is completed.

Rapid drying causes warping, cracking and splintering...
Pressure-treated lumber is shipped to the lumberyard in stacks that are tightly bundled
and damp... sometimes even wet. If you go and pick through a bin of
pressure-treated lumber, you will see some pieces are straight, and others moderately to
wildly warped. The warped pieces are invariably the pieces that were on the
outside of the bundle... exposed to the sun and air and dried on one side. Once
the bundle is broken they twist like Chubby Checker!

Once installed in your project and subjected to freely moving air and the
sun, the same effect occurs. Shrinkage of deck boards can be excessive, in both
length and width, and twisting can loosen railings and floor boards. Railings
can become cracked and splintery, making them uncomfortable to use.

Health and safety...

A certain amount of PT preservative will leach to the surface of the wood
over time. Applying a coating every year or two (once the rain stops
beading) greatly lessens the amount of preservative that leaches to the surface.

Applying a preservative slows drying and inhibits shrinkage and helps
maintain a smoother surface to the wood. The sun takes no prisoners
and even pressure treated wood needs protection from it. Remember, the
preservative protects the wood from mold and mildew, not good old Sol! The preservative should be applied
immediately upon completion of the project or within a month or so if the wood
is especially wet. Be sure that the preservative you
purchase is recommended for use with pressure-treated wood. More about this
in the next section...

Can pressure-treated wood be painted or stained? Definitely!

Stains first...

Many manufacturers carry full
lines of both oil and latex products that can be used on pressure-treated wood.
According to the folks at Cuprinol,
you should wait at least one to two months before staining. You may apply a clear preservative immediately, but it must be a product
manufactured for use on fresh pressure-treated lumber. One such
product is
Wolman Oil-Base RainCoat Clear Water Repellant.

What about painting? Don't even think about
painting fresh pressure-treated wood!

The moisture in it "stacks the deck" against
good paint adhesion. Seal your project with a pressure-treated wood preservative
immediately. Follow the preservative's instructions regarding future painting,
making special note of the amount of time the preservative should weather before
painting.

Applying a sealer can protect against CCA exposure...

According to the EPA, studies show that the application of a
penetrating oil finish can reduce or eliminate exposure to CCA in older decks
and to the chemicals used in newer decks. So it is recommended that all
pressure-treated surfaces that have human contact be coated with an oil finish
as needed. It has been noted in some studies that paints and opaque
exterior stains do not offer the protection of stains that are absorbed more
deeply into the wood.

Tips for working with pressure-treated wood...

Predrill any nail or screw holes within an inch of the end of the
board.
This lessens the chance of splitting the board while fastening
it. Even if it doesn't split when you initially fasten it down without
predrilling, it will very likely do so later as the wood dries out.

Use the right fasteners.
Use only screws or nails that are
galvanized and designed for use with the newer copper-based pressure-treated
wood.

Do not allow any space between boards when laying in a deck floor.
Putting spacers between floor boards is the amateur's biggest mistake.
pressure-treated wood shrinks, even if you coat it with a preservative!
Years ago when it first came on the market, people installed deck floors
like good old untreated Douglas Fir, installing the boards with spacers
between them. Wood shrinkage typically caused 3/4" or wider gaps in the
floor... just the right width to snap off a high heel!

Can deck posts be buried?
Yes, if they are rated for ground contact. This is dependant on local
codes. Some do not allow the burial of posts under any circumstances and
they must be set on (or physically attached to) concrete footings.

Should I install a pressure treated wood deck with the
boards "bark up" or "bark down"?

If
you look at the end grain of any board, you'll notice that the rings have a
particular curve to them. "Bark side" refers to the side of the board that
the rings curve away from. In other words, "bark-side up" would be a
deck board that has the visible grain curve downward. With
pressure-treated southern yellow pine (the most common type) you might even see
a little bark on some pieces.

There has been lots of debate on this issue because of a process called
"cupping". Cupping refers to the tendency of a board to bend across its
width as it dries. Ideally, you would want all the deck boards to cup
downwards so any rain would run off them rather than collect on the wood.

Some people assert that the ONLY way to install deck board is "bark down".
The rationale is that a board in laboratory conditions resting across a couple
of sawhorses will tend to cup towards the bark side as it dries out. This
is undisputed fact and this principle used in cabinetmaking when edge-joining
boards so the cupping in one board is counteracted by the reverse orientation of
the next board and so on and so on. This would make you think that wood
decks should be installed with the bark side down, right? If it were only
that simple.

The truth is not all boards react in the "wild" as they do in the laboratory
or the woodworking shop. For example, unlike redwood or cedar which are
installed dry, pressure-treated wood is installed damp or even soaking wet!
The excess moisture from the preservative treatment can cause excess cupping as
it dries, whether it is installed with the bark up or down! In other
words, the simple drying action of the sun and wind can cause the top of the
board to dry faster than the bottom, causing cupping regardless of the exposed
top.

I used to think that bark up was the rule, but over the years I've come to
realize that it doesn't matter as much as I thought. So now I use a couple
of general principles to determine which side of the board will be the top.

The first and often the most important is to observe the amount
of cupping already occurring on the board. Most boards right
from the lumberyard will show at least a small amount of cupping. By
installing these boards so the peak of the cup is upwards, the board will
tend to flatten out as it dries.

Coat your deck surface with a clear preservative as soon as possible.
Sealing the top of the deck surface slows down the rate of evaporation so
most of the evaporation will occur on the underside of the deck, causing the
board to peak upwards... your desired result.

If you are unsure and the board is very flat to begin with, go with your
gut and put the best looking side of the wood up. Based on the
conflicting information out there, you've got a 50-50 chance of being
right!

Written by Jerry Alonzy

Jerry Alonzy, a.k.a. the Natural Handyman, has been an active handyman for over 30 years with experience in most areas of home repair and renovation.

As a do-it-yourself author and web developer since 1995, he has been featured in USA Today, the Today Show and on radio shows, magazines, newspapers and websites. His material appears widely on the web, but primarily on his website... The Natural Handyman. You can also find him on Google+.